Gas Assisted Injection Molding

- Jul 11, 2018-

The gas-assisted injection molding system uses an inert gas (usually nitrogen) directly injected into the plasticized plastic in the cavity through the sectional pressure control system to expand the interior of the plastic part to create a hollow shape, but still keep the surface of the product intact.


Gas-assisted injection molding can be considered as a variant of hollow blow molding. The process is to inject a precisely proportioned plastic melt into the mold cavity, which is called “under-injection molding”. Directly inject a certain volume and pressure of high-pressure nitrogen into the molten plastic, and the gas spreads in the direction of the least resistance under the plastic melt.


Since the plastic part of the mold wall has a low temperature and a high surface viscosity, and the thick part of the central plastic melt has a high temperature and a low viscosity, the gas is easy to penetrate and emptied the central plastic melt, and the thickness of the part is thick. The middle part forms a middle air passage, and the molten plastic which is evacuated by the gas is pushed by the gas pressure to the end of the mold until it fills the mold cavity, and the compressed gas compresses and shrinks the plastic melt in the cooling stage. After the product is cooled and solidified, the gas is discharged, and then the mold is ejected.


There are two main types of gas-assisted injection molding methods:


First, the method of closed gas injection (SEALED INJECTION GAS).


It is a method of directly injecting gas into the cavity to make the finished plastic hollow. There is no need to use a live valve, but the gas-assisted nozzle is installed in the mold by simple mold processing.


On the same mold, there may be a single or multiple places where the gas is injected. This depends on the needs of the same product, and requires a good effect on the product and greater flexibility in providing product design.


Second, the method of injecting air from the injection molding machine (IN-GAS NOZZLE).


Install a special closed gas injection nozzle on the injection molding machine.